The present invention relates to fluid supply pipes for supplying a fluid, such as a liquid or gas. In particular, the present invention relates to fluid supply pipes in which the amount of electric charge that builds up in the fluid when the fluid passes through the fluid supply pipes can be maintained within a proper range.
Fuel supply systems have been recently developed in which a fuel pump and a fuel filter are disposed within a fuel tank that is installed in a location some distance away from an internal combustion engine of a vehicle, in which fuel is drawn out of the fuel tank by the fuel pump and is supplied to the internal combustion engine through a fuel supply pipe. FIG. 8 schematically shows a construction of an example of such a known fuel supply system. The fuel supply system shown in FIG. 8 is of a type that controls the fuel pump such that the pressure of the fuel that is supplied to a fuel injection valve is maintained at a desired pressure.
As shown in FIG. 8, an inlet pipe 20 and an exhaust pipe 30 are connected to an internal combustion engine 10, and an inlet valve 13 and an exhaust valve 14 are disposed in the engine 10. Air is filtered through an air cleaner 21 and is supplied into inlet pipe 20 via a throttle valve 22. Throttle valve 22 controls the air flow rate. Fuel is also supplied from a fuel injection valve 40 into inlet pipe 20. The air and the fuel are mixed within inlet pipe 20 and are supplied into each cylinder through inlet valve 13. Further, combustion gas within the cylinder is exhausted into exhaust pipe 30 through exhaust valve 14.
Further, fuel pump 42 (which is typically constructed in modules that are integrally formed with a fuel filter) is disposed within a fuel tank 41 and serves to draw fuel out of fuel tank 41. Fuel is supplied from fuel tank 41 to a fuel injection valve 40 for each cylinder through a fuel supply pipe 73 and a delivery pipe 45.
Fuel supply pipe 73 includes a fixed fuel supply pipe 73b that is fixedly attached to the vehicle body and also includes connecting fuel supply pipes 73a, 73c, which connect fixed fuel supply pipe 73b to fuel pump 42 and delivery pipe 45. Fixed fuel supply pipe 73b comprises a metal, such as a conductive stainless steel. Fixed fuel supply pipe 73b is normally attached to the vehicle body by an elastic insulating element, such as plastic, in order to protect the fuel supply pipe 73b from vibrations. Connecting fuel supply pipes 73a, 73c comprise rubber. The use of connecting fuel supply pipe 73a facilitates removal and attachment of fuel pump 42. Further, connecting fuel supply pipes 73a, 73c, which comprise rubber, can absorb vibrations from the vehicle body and the engine 10.
A control unit (ECU) 60 executes various instructions based on detected signals that are transmitted from a fuel pressure sensor for detecting the fuel pressure, an intake pressure sensor for detecting the intake air pressure, an intake air temperature sensor for detecting the intake air temperature, a water temperature sensor for detecting the cooling water temperature and a sensor for detecting the opening amount of the throttle valve. For example, control unit 60 executes instructions to control the opening amount of throttle valve 22 in order to control the amount of intake air, instructions to control the opening and closing of fuel injection valve 40 in order to supply fuel into the cylinder, and instructions to control fuel pump 42 in order to maintain the fuel pressure at a desired pressure.
However, connecting fuel supply pipes 73a, 73c, which are made of rubber, deteriorate with time and thus require maintenance, such as replacement. Therefore, instead of using a rubber fuel supply pipe, it may be considered to use a resin fuel supply pipe that is easy to make and does not require maintenance.
When fuel passes through a rubber or resin fuel supply pipe, the fuel flows against the fuel supply pipe. Because of friction, the fuel and the fuel supply pipe become electrically charged. When a resin fuel supply pipe is used, a larger amount of electric charge is built up by such friction. Connecting a ground wire to the fuel supply pipe can discharge electric charge built up on the fuel supply pipe. However, electric charge built up in the fuel cannot be readily discharged. Therefore, if, for example, fuel that has been charged by passing through connecting fuel supply pipe 73a shown in FIG. 8 then passes through fixed fuel supply pipe 73b made of metal, fixed fuel supply pipe 73b is inductively charged. Electric charge inductively built up on fixed fuel supply pipe 73b is discharged to the vehicle body, the operator or the like. At this time, because fixed fuel supply pipe 73b has a low bulk resistivity, the electric charge may be rapidly discharged and a spark discharge may be generated. If spark discharge is generated on fixed fuel supply pipe 73b, fixed fuel supply pipe 73b may deteriorate, and operations by the operator may be disturbed.
It is, accordingly, an object of the present invention to maintain within a proper range the amount of electric charge that builds up in the fluid when the fluid passes through a fluid supply pipe.
Another object of the invention is to maintain within a proper range the amount of electric charge that builds up in the fluid when the fluid passes through the fluid supply pipe and also to maintain within a proper range the electric discharge energy that is generated when the electric charge built up on the fluid supply pipe is discharged.
In a preferred embodiment of the invention, the bulk resistivity of the fluid supply pipe is chosen to be 1011 xcexa9xc2x7cm or less. By using this fluid supply pipe, the amount of electric charge that builds up in the fluid when the fluid passes through the fluid supply pipe can be maintained within a proper range.
In another preferred embodiment of the invention, the bulk resistivity of the fluid supply pipe is chosen to be within the range from 107 to 1011 xcexa9xc2x7cm. By using this fluid supply pipe, the amount of electric charge that builds up on the fluid when the fluid passes through the fluid supply pipe can be maintained within a proper range. Also, the electric discharge energy that is generated when the electric charge built up on the fluid supply pipe is discharged can be maintained within a proper range.
In a still another preferred embodiment of the invention, the fluid supply pipe has at least two layers. The bulk resistivity of the innermost layer is chosen to be within the range from 107 to 1011 xcexa9xc2x7cm and the bulk resistivity of the outermost layer is chosen to be 1012 xcexa9xc2x7cm or more. By using this fluid supply pipe, even if the fluid supply pipe is multi-layered, the amount of electric charge that builds up in the fluid when the fluid passes through the fluid supply pipe can be maintained within a proper range. Additionally, the electric discharge energy that is generated when the electric charge built up on the fluid supply pipe is discharged can be maintained within a proper range.
Further, in the preferred embodiments of the invention, the fluid supply pipe is made of a resin.
The present invention will be more apparent from the following detailed description of the best modes for performing the invention.